Question

During this experiment, two different concentrations of potassium thiocyanate (KSCN) are used. Part I uses a large concentration (~1 M) while Part II uses a much smaller concentration (~0.0025 M). Why are these respective concentrations required? Select all that apply. (could have more than one answer)

	a)Part II of this experiment necessitates a lower concentration to ensure that the product does not decompose of er the course of the data collection period.
	b)In order to study the equilibrium state of the reaction (Part II), the concentrations of both reactants need to be similar so that neither reactant will be in great excess.
	c)A large excess of SCN- ions are needed in Part I to push the equilibrium to the right (towards the product) to make sure all of the Fe3+ ions are converted to Fe(SCN)2+.
	d)The excess of KSCN in Part I is needed because the Fe3+ concentration is also much higher. The higher concentration is needed to see an acceptable absorbance value for the Fe(SCN)2+ solution in Part I.

Answer 1

Correct answers are :

(b) In order to the equilibrium state of the reaction (Part II), the concentrations of both reactants need to be similar so that neither reactant will be in great excess.

(c) A large excess of SCN^- ions are needed in Part I to push the equilibrium to the right (towards the product) to make sure all of the Fe³⁺ ions are converted to Fe(SCN)²⁺.

Explanation

In part I of the experiment, we need to create a calibration curve. Hence, large excess of SCN^- reactant is needed to push the equilibrium to the right.

In part II, similar concentration of reactants are required to simulate the actual conditions of nature.